The invention relates to methods and compositions for increasing the anaerobic working capacity of muscle and other tissues.
Natural food supplements are typically designed to compensate for reduced levels of nutrients in the modern human and animal diet. In particular, useful supplements increase the function of tissues when consumed. It can be particularly important to supplement the diets of particular classes of animals whose the normal diet may be deficient in nutrients available only from meat and animal produce (e.g., human vegetarians and other animals consume an herbivorous diet).
For example, in the sporting and athletic community, natural food supplements which specifically improve athletic ability are increasingly important, such as supplements that promote or enhance physical prowess for leisure or employment purposes. In another example, anaerobic (e.g., lactate-producing) stress can cause the onset of fatigue and discomfort that can be experienced with aging. Anaerobic stress can also result from prolonged submaximal isometric exercise when the local circulation is partially or totally occluded by the increase in intra-muscular pressure (e.g., during rock climbing, free diving, or synchronized swimming). Excessive lactate production can result in the acidification of the intracellular environment.
Creatine (i.e., N-(aminoiminomethyl)-N-glycine, N-amidinosarcosine, N-methyl-N-guanylglycine, or methylglycocyamine) is found in large amounts in skeletal muscle and other "excitable" tissues (e.g., smooth muscle, cardiac muscle, or spermatozoa) characterized by a capacity for a high and variable energy demand. Creatine is converted into phosphorylcreatine in energy-generating biochemical pathways within cells. In mammalian skeletal muscle, the typical combined content of creatine (i.e., creatine and phosphorylcreatine) may vary from less than 25 to about 50 mmol per kilogram fresh muscle (i.e., 3.2 to 6.5 grams per kilogram fresh muscle).
Creatine formed is formed in the liver and taken up into tissues, such as muscle, by means of an active transport system. Creatine synthesis in the body may also be augmented by the ingestion of creatine present in meat (e.g., 5-10 milligrams per kilogram body weight per day in the average meat-eating human and approximately zero in a vegetarian diet).
During sustained intensive exercise, or exercise sustained under conditions of local hypoxia, the accumulation of hydronium ions formed during glycolysis and the accumulation of lactate (anaerobic metabolism) can severely reduce the intracellular pH. The reduced pH can compromise the function of the creatine-phosphorylcreatine system. The decline in intracellular pH can affect other functions within the cells, such as the function of the contractile proteins in muscle fibers.
Dipeptides of beta-alanine and histidine, and their methylated analogues, include carnosine (beta-alanyl-L-histidine), anserine (beta-alanyl-L-1-methylhistidine), or balenine (beta-alanyl-L-3-methylhistidine). The dipeptides are present in the muscles of humans and other vertebrates. Carnosine is found in appreciable amounts in muscle of, for example, humans and equines. Anserine and carnosine are found in muscle of, for example, canines, camelids and numerous avian species. Anserine is the predominant beta-alanylhistidine dipeptide in many fish. Balenine is the predominant beta-alanylhistidine dipeptide in some species of aquatic mammals and reptiles. In humans, equines, and camelids, the highest concentrations of the beta-alanylhistidine dipeptides are found in fast-contracting glycolytic muscle fibers (type IIA and IIB) which are used extensively during intense exercise. Lower concentrations are found in oxidative slow-contracting muscle fibers (type I). See, e.g., Dunnett, M. & Harris, R. C. Equine Vet. J., Suppl. 18, 214-217 (1995). It has been estimated that carnosine contributes to hydronium ion buffering capacity in different muscle fiber types; up to 50% of the total in equine type II fibers.